1. Field of the Invention
The present invention relates to anti-oxidant containing polyolefin compositions including titanium dioxide-coated mica particles with a coating of silica and alumina calcined thereon to prevent yellowing of the polyolefin compositions.
2. Description of the Prior Art
Many pearlescent or nacreous pigments are based on micaceous substrates which have been coated with a metal oxide layer. As a result of reflection and refraction of light, these pigments exhibit pearl-like luster and depending on the thickness of the metal oxide layer, they can also exhibit interference color effects.
Among the pearlescent pigments encountered most often on a commercial basis are titanium dioxide-coated mica pearlescent pigments. However, often such pigments are incompatible with the polyolefin compositions in which they are incorporated. For instance, inorganic pigments, such as titanium dioxide-coated mica pigments, frequently cause yellowing of anti-oxidant containing polyolefin compositions in which they are contained.
U.S. Pat. No. 4,209,430 relates to a process for suppressing yellowing in thermoplastic polyolefins containing a phenolic anti-oxidant and TiO.sub.2 pigment by adding a phosphorylated polyene either directly to the polyolefin or as a coating on the pigment.
U.S. Pat. No. 4,357,170 reviews various solutions to the problem of yellowing of titanium dioxide pigments in polymeric compositions such as polyethylene in the presence of additives such as phenolic antioxidants.
U.S. Pat. No. 4,494,993 relates to a pigment in which a homogeneous mixture of titanium dioxide, silicon dioxide and aluminum oxide is coated on mica flakes.
It has been found that the prior art solutions to the yellowing of anti-oxidant containing polyolefin compositions are not totally effective. Some yellowing of the polyolefin compositions can still be seen. Therefore, it is desirable to develop a titanium dioxide-coated mica containing polyolefin composition which avoids the disadvantages of the prior art described above, affording the advantages of substantially improving control of the yellowing phenomena frequently encountered.
It is accordingly an object of this invention to provide anti-oxidant containing polyolefin compositions including titanium dioxide-coated mica particles having a coating of silica and alumina calcined thereon to prevent yellowing of the polyolefin composition. Another object of the present invention is to provide a method of preventing the yellowing of an anti-oxidant containing polyolefin composition.
These and other objects of the invention will become apparent to those skilled in this art from the following detailed description.